The present invention relates to a process for removing sulfides. The invention has particular application to the removal of sulfides from hydrogen sulfide gas to produce hydrogen gas and sulfur.
Hydrogen sulfide is often present in large quantities in natural gas reserves, petroleum and coal. Its removal is essential to clean up fossil fuels. Its conversion to valuable products is desirable to minimize the cost of its removal. One approach that has been attempted is to convert hydrogen sulfide into hydrogen gas and sulfur electrochemically.
Previous investigations on the electrolysis of hydrogen sulfide led to the passivation of the anode in the first few minutes of the electrolysis. See U.S. Pat. No. 1,891,974, U.S. Pat. No. 3,409,520, and U.S. Pat. No. 4,544,461. To avoid this problem, researchers have attempted indirect electrolysis of hydrogen sulfide in which iodine precipitates the sulfur, and electrochemical methods regenerate the iodine and produce hydrogen. See U.S. Pat. No. 2,839,381 and Kalina et al., Int. J. Hydrogen Energy, Vol. 10, p. 157 (1985). It is reported that the sulfur obtained by this indirect process is plastic in nature and needs further purification.
Electrolysis of hydrogen sulfide in aqueous alkaline solutions at 85.degree. C. using carbon electrodes has also been reported. See Dandapani et al., in "Advancing Toward Technology Breakout in Energy Conversion," a Symposium of the 21st Intersociety Energy Conversion Engineering Conference, Vol. 1, p. 262 (1986). The reported process saturates an anodic compartment with H.sub.2 S gas. This appears to lead to passivation of the anode.
There is a need for a low temperature electrochemical method for removing sulfides from sulfide containing solutions that is not restricted by passivation of the anode. There is a need for such a method that produces hydrogen and sulfur from hydrogen sulfide gas with an efficiency that does not decrease with time. The process of the present invention provides such a method.